Microfiber-containing fiber reinforced facer mats and method of making

ABSTRACT

Fiber-reinforced composite mats are described that include a non-woven web of fibers. The web of fibers may include a first group of fibers having an average fiber diameter from about 8 μm to about 25 μm, and a second group of fibers having an average fiber diameter from about 0.5 μm to about 6.5 μm. A binder bonds together the non-woven web of fibers into the fiber reinforced composite having an air permeability of 250 cfm/ft 2  or less. Also described are gypsum boards that include one or more facers affixed to at least one surface of the gypsum board. The facers may be made from the above, described fiber-reinforced composite mats.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to co-assigned U.S. Pat. Nos.7,829,488 issued Nov. 9, 2010, and 7,258,759 issued Aug. 1, 2007. It isalso related to co-assigned U.S. patent application Ser. No. 12/383,027filed Mar. 19, 2009. The entire contents of these patent and patentapplication are herein incorporated by reference for all purposes.

FIELD OF THE INVENTION

Embodiments of the invention relate to construction materials used inbuilding construction, including fiber-reinforced composite facedconstruction board, such as gypsum board. The fiber-reinforced compositefacers on exposed surfaces of the construction board may include a glassfiber mat made from a blend of large and small diameter glass fibersbonded together with a binder, such as an organic or inorganic binder.

BACKGROUND OF THE INVENTION

Wallboard formed of a gypsum core sandwiched between facing layers isused in the construction of virtually every modern building. In itsvarious forms, the material is employed as a surface for walls andceilings and the like, both interior and exterior. It is relatively easyand inexpensive to install, finish, and maintain, and in suitable forms,is relatively fire resistant.

Paper-faced wallboard (e.g., gypsum wallboard) is commonly used forfinishing interior walls and ceilings. Gypsum wallboard and gypsumpanels are traditionally manufactured by a continuous process. In thisprocess, a gypsum slurry is generated and deposited on a continuouslyadvancing, lower facing sheet, such as kraft paper. A continuouslyadvancing upper facing sheet is laid over the gypsum and the edges ofthe upper and lower facing sheets are pasted to each other with asuitable adhesive. The facing sheets and gypsum slurry are passedbetween parallel upper and lower forming plates or rolls in order togenerate an integrated and continuous flat strip of unset gypsumsandwiched between the sheets. Such a flat strip of unset gypsum isknown as a facing or liner. The strip is conveyed over a series ofcontinuous moving belts and rollers for a period of several minutes,during which time the core begins to hydrate. The process isconventionally termed “setting,” since the rehydrated gypsum isrelatively hard. During each transfer between belts and/or rolls, thestrip is stressed in a way that can cause the facing to delaminate fromthe gypsum core if its adhesion is not sufficient.

While paper is widely used as a facing material for gypsum boardproducts because of its low cost, many applications demand waterresistance that paper facing cannot provide. Upon exposure to watereither directly in liquid form or indirectly through exposure to highhumidity, paper is highly prone to degradation, such as by delamination,that substantially compromises its mechanical strength. Gypsum productstypically rely on the integrity of the facing as a major contributor totheir structural strength. Consequently, paper-faced products aregenerally not suited for exterior or other building uses in whichexposure to moisture conditions is presumed.

In addition, there is growing attention being given to the issue of moldand mildew growth in building interiors and the potential adverse healthimpact such activity might have on building occupants. The paper facingof conventional gypsum board contains wood pulp and other organicmaterials that may act in the presence of moisture or high humidity asnutrients for such microbial growth. A satisfactory alternative facingmaterial less susceptible to growth is highly sought.

A further drawback of paper-faced gypsum board is flame resistance. In abuilding fire, the exposed paper facing quickly burns away. Although thegypsum itself is not flammable, once the facing is gone the board'smechanical strength is greatly impaired. At some stage thereafter theboard is highly likely to collapse, permitting fire to spread to theunderlying framing members and adjacent areas of a building, withobvious and serious consequences. A board having a facing lesssusceptible to burning would at least survive longer in a fire and thusbe highly desirable in protecting both people and property.

To overcome these and other problems, alternatives to paper facing havebeen proposed. For example, exterior insulation systems have beendeveloped that include a fibrous mat-faced gypsum board. However, gypsumboard products incorporating the fibrous mats have proven to havecertain drawbacks: Some persons are found to be quite sensitive to thefiberglass mat, and develop skin irritations and abrasions when exposedto the mat at various stages, including the initial production of themat, the manufacture of composite gypsum board with the mat facing, andduring the cutting, handling, and fastening operations (e.g., with nailsor screws) that attend installation of the end product during buildingconstruction. Handling of the mat, and especially cutting, is believedto release glass fibers responsible for the irritation. The fibers mayeither become airborne or be transferred by direct contact. As a result,workers are generally forced to wear long-sleeved shirts and long pantsand to use protective equipment such as dust masks. Such measures areespecially unpleasant in the sweaty, hot and humid conditions oftenencountered either in manufacturing facilities or on a constructionjobsite.

In addition, many commercial fiber-faced construction boards have asurface roughness that makes them difficult to finish satisfactorily bynormal painting, because the texture of the mat remains perceptiblethrough the paint. The fibers in the mat themselves give rise to variousasperities, and to additional, larger sized irregularities often termedin the industry with descriptives such as “orange peel”, “cockle”, orsimilarly evocative terms describing surface non-planarity. Theperceived smoothness of a board surface is the result of a complexinterplay between various topographic features of the board, includingthe size, depth, spacing, and regularity of the features. Although someof these attributes may be quantified somewhat using image analysistechniques, visual comparison, especially under obliquely incidentlight, is more than sufficient for comparing the relative smoothness ofdifferent surfaces.

Moreover, making the construction board may involve the deposition of arelatively wet slurry onto the fiber-reinforced mat, which is generallyfound to result in considerable intrusion of the slurry through the matand onto the faced surface. Prevention of this excess intrusiontypically requires very careful control of the slurry viscosity, which,in turn, frequently leads to other production problems. Alternativemats, which inherently limit intrusion, yet still have sufficientpermeability to permit water to escape during the formation and heatdrying of the construction board are thus eagerly sought as a simpleralternative. These and other problems are address in the presentapplication.

BRIEF SUMMARY OF THE INVENTION

Fiber-reinforced composite mats for use in construction board and otherbuilding materials are described, as well as processes of making themats, boards, and materials. The mat-faced construction boards may haveone or more of a smoother surface, a stronger internal bond to preventdelamination of the facer when subjected to prolonged wetness afterinstallation, a surface requiring less paint to produce an aestheticallyacceptable finished wall, etc., and better flame and mold resistance.

Exemplary fiber-reinforced composite mats may include a blend of largeand small fibers to give the mats lower air permeability thanconventional mats for construction board facer applications. Thefiber-reinforced composite mats may be used as facers for constructionboard, such a gypsum board having a layer of set gypsum with a firstface and a second face and the fiber-reinforced composite mat affixed asa facer to at least one of the faces. The gypsum board may be used for anumber of purposes in building construction, such as a surface materialfor walls and ceilings and as an underlayment for floors, roofs, and thelike. The present construction board may find application in bothinterior and exterior environments. As a result of the selection offibers in the facing, the board has a smooth, uniform surface thatreadily accepts paint or other surface treatments to provide a pleasingaesthetic appearance.

The low air permeability of the mats (typically 250 cfm/ft² at 0.5″ w.c.or less) reduces bleedthrough from aqueous slurries of constructionmaterials applied to the mat. These slurries may include calciumsulfate, calcium sulfate hemi-hydrate, and/or hydraulic setting cementthat are often used to make gypsum board, among other construction boardmaterials. The low air permeability of the mats permits slurrycompositions with lower viscosity to be applied without increasing therate at which the slurry bleeds through the mat to create a rough,uneven surface on the exposed faces of the construction board.

Embodiments of the invention include fiber-reinforced composite matsthat include a non-woven web of fibers. The web of fibers may include afirst group of fibers having an average fiber diameter from about 8 μmto about 25 μm, and a second group of fibers having an average fiberdiameter from about 0.5 μm to about 6.5 μm. A binder bonds together thenon-woven web of fibers into the fiber reinforced composite having anair permeability of 250 cfm/ft² or less.

Embodiments of the invention further include gypsum board having atleast one fiber-reinforced composite facers affixed to at least onesurface of the gypsum board. The fiber-reinforced facer may include anon-woven web of fibers, wherein the fibers may be a blend of a firstgroup of fibers having an average fiber diameter from about 8 μm toabout 25 μm, and a second group of fibers having an average fiberdiameter from about 0.5 μm to about 6.5 μm. The fiber-reinforced facersmay also include a binder that bonds together the non-woven web offibers into the fiber reinforced composite. The composite may have anair permeability of 250 cfm/ft² or less.

Embodiments of the invention still further include processes formanufacturing a fiber-reinforced composite. The processes may includeblending a first group of fibers having an average fiber diameter fromabout 8 μm to about 25 μm with a second group of fibers having anaverage fiber diameter from about 0.5 μm to about 6.5 μm to form anon-woven web of fibers. The non-woven web of fibers may be contactedwith a binder solution to form a wet mat, which may be cured to form afiber-reinforced composite mat. The fiber-reinforced composite mat mayhave an air permeability of 250 cfm/ft² or less.

In further embodiments, an aqueous slurry may be applied to a surface ofthe fiber-reinforced composite mat. The slurry may include one or morematerials such as calcium sulfate, calcium sulfate hemi-hydrate, andhydraulic setting cement.

In still further embodiments, a first facer made of the above-describedfiber-reinforced composite mat may be provided, and the aqueous slurrymay be distributed on the first facer to form a layer. A second facer(which may be made of the same fiber-reinforced composite mat as thefirst facer or a different material) may be applied on top of the layerto form a laminate. The laminate may be cut into specified lengths,which may be dried to form dried pieces that have a smoothnesssufficient to be directly painted. Exemplary dried pieces includeinterior gypsum board for building construction.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the invention. The features and advantages ofthe invention may be realized and attained by means of theinstrumentalities, combinations, and methods described in thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings wherein like reference numerals are usedthroughout the several drawings to refer to similar components. In someinstances, a sublabel is associated with a reference numeral and followsa hyphen to denote one of multiple similar components. When reference ismade to a reference numeral without specification to an existingsublabel, it is intended to refer to all such multiple similarcomponents.

FIG. 1 shows a simplified cross-sectional view of a mat-facedconstruction board according to embodiments of the invention;

FIG. 2 shows selected steps in a process for manufacturing afiber-reinforced composite according to embodiments of the invention;and

FIG. 3 shows selected steps in a process for manufacturing a facedconstruction board according to embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Construction boards (such as hydraulic set and cementitious board) aredescribed having front and back large surfaces, at least one of which isfaced with a fiber-reinforced composite mat. By hydraulic set is meant amaterial capable of hardening to form a cementitious compound in thepresence of water. Typical hydraulic set materials include gypsum,Portland cement, pozzolanic materials, and the like.

Exemplary Fiber-Reinforced Composite Mat-Faced Construction Board

Referring now to FIG. 1, there is shown generally at 30 a sectional viewacross the width direction of one embodiment of a fiber-reinforcedcomposite mat-faced construction board. In the embodiment shown, theboard has a layer of set gypsum 28 which is sandwiched between first andsecond fibrous mats 14, 20, and bonded thereto. Two right-angled foldsare formed in each lateral edge of first mat 14, a first upward fold anda second inward fold. The two folds are separated by a small distance,whereby the thickness of board is generally determined. The second foldsdefine longitudinally extending strips 16 and 18 that are substantiallyparallel to the main part of the mat. A second fibrous mat 20 covers theother side of the set gypsum core 28. The respective lateral edges ofsecond mat 20 are affixed to strips 16 and 18, preferably with adhesive22, 23. Ordinarily board 30 is installed with the side bearing mat 14facing a finished space. The board is advantageously ready for painting,but other finishing forms such as plaster, wallpaper or other known wallcoverings may also be applied with a minimum of surface preparation.

The mats for one or both of the large faces of the gypsum board mayinclude a non-woven web bonded together with a resinous binder. The webcomprises chopped continuous glass fibers, that may be a blend of largerdiameter fibers (e.g., chopped strand fibers, staple fibers) and smallerdiameter fibers (e.g., microfibers). The larger diameter fibers may havean average fiber diameter of 7 μm or more. Exemplary size ranges for thelarger diameter fibers may include about 8 μm to about 25 μm, about 10μm to about 20 μm, about 12 μm to about 14 μm, about 13 μm, etc. Thesmaller diameter fibers may have an average size range of less than 7μm. Exemplary size ranges for the smaller diameter fibers from about 0.5μm to about 6.5 μm, about 2 μm to about 5 μm, about 2.5 μm, etc.

Embodiments include blending a larger quantity of the larger diameterfibers with a smaller quantity of the smaller diameter fibers to makethe non-woven fiber web. For example, the larger diameter fibers maymake up more than half the total weight of the fiber blend in the web.Exemplary quantities of the larger diameter fibers may include about 70wt. % to about 90 wt. % of the total weight of the fibers (e.g., about80 wt. %). Exemplary quantities of the smaller diameter fibers mayinclude about 10 wt. % to about 30 wt. % of the total weight of thefibers (e.g., about 20 wt. %).

The fiber length of the larger diameter fibers and the smaller diameterfibers used in the blend may be the same or different. Exemplary fiberlengths may include about 6 mm to about 18 mm. The web of fibers mayalso include fibers that are broken into two or more pieces and smallglass fibers (e.g., less than 1 mm), chips, and flakes.

The web of fibers may include chopped strand fibers, staple fibers, orboth. Staple fibers are usually made by processes such as rotaryfiberization or flame attenuation of molten glass. They typically have awider range of lengths and fiber diameters than chopped strand fibers.

Surfaces of the present construction boards may have an improved “hand,”i.e., an improved subjective feel, and better accepts surface treatmentsbecause of its greater smoothness. In contrast to conventionalconstruction boards where even substantial amounts of paint applied inmultiple coats can still leave the facing mat visible and aestheticallyunpleasing, the present boards may be finished to provide an aestheticand functional surface with less paint and the associated labor toprepare the surface and apply the paint or other desired finish,wallpaper or other coating, or the like.

The glass used in the fibers of the present webs may include one or moretypes of glass selected from the group consisting of E, C, and T typeand sodium borosilicate glasses, and mixtures thereof. C glass typicallyhas a soda-lime-borosilicate composition that provides it with enhancedchemical stability in corrosive environments, and T glass usually has amagnesium aluminosilicate composition and especially high tensilestrength in filament form. E glass, which is sometimes called electricalglass, generally has a calcium aluminoborosilicate composition and amaximum alkali content of about 2.0%. The chopped fibers of largeraverage diameter can have varying lengths, but more commonly aresubstantially of similar length. E glass fiber has sufficiently highstrength and other mechanical properties to produce acceptable mats andis relatively low in cost and widely available. Exemplary sizes of Eglass fibers may include an average fiber diameter of about 9 μm toabout 13 μm, and a length ranging from about 6 to 12 mm.

The aforementioned glass fibers may be bound together with an organic orinorganic binder. This may include flame and water resistant resinousbinders such as urea formaldehyde, modified urea formaldehyde, acrylicresins, melamine resins, homopolymers or copolymers of polyacrylic acid;crosslinking acrylic copolymers (e.g., acrylic copolymers having a glasstransition temperature (GTT) of at least about 25° C.); crosslinkedvinyl chloride acrylate copolymers (e.g., copolymers having a GTT ofabout 113° C. or less), among other types of binders. A lower GTT maypromote better softness and smoothness of the mat surface, but tensilestrength may be improved with a higher GTT. Exemplary GTT may range fromabout 15° C. to 45° C. Exemplary binder systems may further includeaqueous modified and plasticized urea formaldehyde resin binders.

The binder may include an effective amount of a water repellant to limitthe intrusion of aqueous slurry during board production. For example,vinyl acrylate latex copolymers may further incorporate stearylatedmelamine for improvement in water repellency. Exemplary concentrationsof the stearylated melamine may include about 3 wt. % to 10 wt. %,(e.g., about 6 wt. %). Aqueous stearylated melamine emulsions areavailable commercially from Omnova Solutions Inc., under the tradenameSEQUAPEL™ 409. The stearylated melamine is in liquid form having asolids content of about 40 wt. percent and is mixed with a suitablecopolymer latex and water to prepare binders for the mats. This materialmixture has a pH of about 9, a viscosity of about 45 centipoises and isanionic. In some instances, construction board faced withfiber-reinforced composite mat that incorporates a water repellant inthe binder may also be more resistant to abrasion than similar mats thatdon't use a water repellant.

Exemplary binders for the fiber-reinforced composite mats may include anacrylate copolymer binder latex with a GTT of about 25° C. These bindersare commercially available from Noveon, Inc. of Cleveland, Ohio, underthe tradename Hycar™ 26138. As delivered, this acrylate copolymer latexhas a solids content of about 50 weight percent solids, and in someinstances may be diluted with water to a concentration about 25 wt.percent solids before being applied to the web of fibers. A crosslinkermay be added to the acrylate binder system, such as a melamineformaldehyde crosslinker in a concentration of up to about 10 wt. %(e.g., about 2 wt. % to about 5 wt. % of the binder solution weight). Insome embodiments, the webs of fibers bound with the acrylate copolymerlatex is smoother and the mat thinner for equivalent weight andproperties than with other known binders. The binder systems do notrequire fluorochemical emulsions, which can be expensive.

The amount of acrylate copolymer latex binder (and any optionalcross-linker) left in the wet mat during manufacture can be determinedby a loss on ignition (LOI) test, the result thereof being specified asa percentage of the dry weight of the finished mat. Exemplary amounts ofbinder in the final mat, based on its dry weight, may range from about15 wt. % to 35 wt. % (e.g., about 20 wt. % to about 30 wt. %; about25±2.5 wt. %, etc.). The upper limit may be dictated by processconstraints and cost, while the minimum is required for adequate tensilestrength.

Optionally the fiber-reinforced mats may further contain fillers,pigments, or other inert or active ingredients either throughout the mator concentrated on a surface. For example, the mat may contain effectiveamounts of fine particles of limestone, glass, clay, coloring pigments,biocide, fungicide, intumescent material, or mixtures thereof. Suchadditives may be added for known structural, functional, or aestheticqualities imparted thereby. These qualities include coloration,modification of the structure or texture of the surface, resistance tomold or fungus formation, and fire resistance. Flame retardantssufficient to provide flame resistance may be added (e.g., ASTM StandardE84, Class 1, by the American Society for the Testing of Materials). Abiocide may added to the mat and/or aqueous slurry to resist fungalgrowth, its effectiveness being measurable in accordance with ASTMStandard D3273. The facer mat and gypsum layer may have a very lowcellulosic fiber content from which microbes could derive nutrition. Insome embodiments, any cellulosic fiber present in the mats or gypsum isonly an impurity of other ingredients.

The present construction board may be faced with a fiber-reinforcedcomposite mat having a basis weight ranging from about 0.6 to 2.2 poundsper 100 square feet (e.g., ranging from about 0.9 to 2.2 lbs./100 ft²;about 1.7±0.2 lbs./100 ft², etc.). Exemplary binder content of the driedand cured mats may range from about 10 wt. % to about 35 wt. %, (e.g.,about 15 to about 30 wt. %; about 25±3 wt. %, etc., based on the weightof the finished mat). The basis weight should be large enough to providethe mat with sufficient tensile strength for producing qualityconstruction board. At the same time, the binder content should belimited for the mat to remain sufficiently flexible to permit it to bebent to form the corners of the board, as shown in FIG. 1. Too thick amat may also render the board difficult to cut during installation. Suchcuts are needed both for overall size and to fit the board aroundprotrusions such as plumbing and electrical hardware.

It is conventional in the wallboard industry to characterize mat usingmechanical testing machines with samples about 7.5 cm (3 inches) wide.Tests are conducted with tension applied either in the machine direction(i.e., along the mat's elongated dimension) or in the cross-machinedirection (i.e., along its width). Mats having adequate strength in boththe machine and cross-machine directions are required for producinggypsum board that will withstand the stresses invariably encountered inmanufacturing, handling, shipping, and installing the board. It is alsopreferred that the combined strengths in the two directions be high forthe same reason.

The present fiber-reinforced composite mats are further enhanced bytheir relatively low air permeability. During the construction boardformation process, an aqueous slurry of cementitious material (e.g., oneor more of calcium sulfate, calcium sulfate hemihydrate, and/orhydraulic setting cement) applied to the mats and susceptible tomigrating though the mats and onto its outer surface. In severe cases,the slurry may seep through the mat and drip onto the underlying matsupport that will then require more frequent and involved cleaning.Decreasing the air permeability of the mat also decreases the rate ofmigration of the slurry through the mat, which in-turn reduces theinstances of slurry bleed through that can cause irregularities on theouter surface of the facer and, in severe cases, migration of the slurryunto the underlying processing equipment.

The air permeability of the mat may be measured by the air flow betweenreservoirs separated by the mat. One such test is called the Fraziertest and is further described by ASTM Standard Method D737, with theresults ordinarily being given in units of cubic feet per minute persquare foot (cfm/ft²). The test is carried out at a differentialpressure of about 0.5 inches of water.

The air permeability of the present fiber-reinforced composite mats maypreferably be about 250 cfm/ft² or less. Exemplary air permeabilitylevels for the present mats may include a range of about 250 cfm/ft² toabout 150 cfm/ft²; about 250 cfm/ft² to about 200 cfm/ft²; about 240cfm/ft² to about 220 cfm/ft²; about 235 cfm/ft² to about 225 cfm/ft²;and about 235 cfm/ft² to about 230 cfm/ft², among other exemplaryranges. These air permeabilities produce mats for construction boardthat have a reduced level of bleed through for slurries set toconventional viscosities, which results in an outer facer surface withreduced roughness. In addition to the lower air permeability, theselection of the fiber blends may produce a mat with sufficientsmoothness to permit direct painting without the application of tapesand/or surfacing materials (e.g., plaster) to the facer. Thus, thesemats are well suited as components of construction board such asinterior gypsum board.

Exemplary Processes

FIG. 2 shows selected steps in an exemplary process 200 of manufacturinga fiber-reinforced composite according to embodiments of the invention.The process 200 may include the step 202 of blending a first and secondgroup of fibers to form a non-woven web of fibers. The first group offibers may have an average fiber diameter of about 8 μm to about 25 μm,while the second group of fibers may have an average fiber diameter ofabout 0.5 μm to about 6.5 μm. An exemplary technique for the blendingmay include the forming of a slurry (e.g., an aqueous slurry) with thefibers. The fiber slurry may then be mechanically agitated to dispensethe fibers more homogeneously through the slurry. Following theagitation, the slurry may be dispensed on a moving screen. A vacuum maybe applied to remove a substantial part of the aqueous solution, whichmay be recycled into more solution for the slurry. With a substantialportion of the aqueous solution removed, the non-woven web of fibers isformed on the moving screen.

The non-woven web of fibers may then be contacted with a binder solution204 to form a wet mat. The binder solution may be an aqueous bindersolution applied to the web using, for example, a curtain coater or adip-and-squeeze applicator. Excess binder solution may pass through thescreen supporting the binder-coated wet mat.

The wet mat may then be cured 206 to form the fiber-reinforced compositemat. Exemplary curing techniques may include heating, among othertechniques. Continuing with the moving screen technique described above,heat may be applied following the remove of excess binder though the webof fibers to evaporate any remaining water and cure the polymerprecursors in the binder solution into a polymerized binder that bondstogether the fibers. The heat source may be an oven though which the wetmat is conveyed on the moving screen.

In some embodiments, the process of manufacturing the fiber-reinforcedmat may be a continuous process, with the moving screen providing acontinuous, conveyor-like loop that may be on a slight upward inclinewhile the fiber slurry is deposited thereon. Subsequently, the excessslurry solution is removed and the non-woven web of fibers is conveyedan area where binder solution is applied. Following the spraying,curtain coating, etc., of the binder solution, the wet mat is conveyedon the moving screen though an oven for the drying of the mat andpolymerization of the binder. Exemplary heating conditions may includesubjecting the wet mat to temperatures of about 120° C. to about 330° C.for periods of, for example, 1 to 2 minutes, less than 40 seconds, etc.The final mat may have a thickness of, for example, about 10 mils toabout 30 mils.

Referring now to FIG. 3, selected steps in a process 300 formanufacturing a faced construction board according to embodiments of theinvention is shown. The process 300 includes the step 302 of forming afiber-reinforced composite mat that will act as a first facer for theconstruction board. The fiber-reinforced composite mat may be formedaccording to the processes described above.

The process 300 may further include the step 304 of distributing aslurry of construction material on the first facer to form a layer. Theslurry may be an aqueous slurry that includes one or more materialsselected from the group of calcium sulfate (CaSO₄), calcium sulfatehemihydrate (CaSO₄.½H₂O), and hydraulic setting cement. The slurry mayalso optionally include reinforcing fibers, process control agents,biocides, flame retardants, and water repellants, among other slurryadditives.

The process 300 may also include the step 306 of applying a second faceronto the top of the layer formed by the aqueous slurry to form alaminate of the slurry material sandwiched between the first facer andthe second facer. The laminate may be separated 308 into individualpieces. Separation techniques may include cutting the laminate intosheets having standard dimensions for commercially sold constructionboard (e.g., widths of at least 2 feet, 4 feet, etc.; and lengths of atleast 2 feet (e.g., about 8 ft to about 12 ft, etc.)). The individualpieces of laminate may then be dried 310 for form the final constructionboard that is faced to provide a smoothness sufficient to permit thedried article to be directly painted.

The present construction boards exhibit a number of desirable qualities:The fibrous mat used results in a surface that is smoother and moreamenable to painting or other surface finishing processes, making themexcellent candidates for interior construction board. The mat is alsomore flexible, facilitating the bending operations needed to fold thefacer around the core during production, as illustrated for mat 14 inFIG. 1. Moreover, board incorporating the fibrous mat of the inventionhas a reduced tendency to generate irritating dust during cutting andhandling.

Experimental

The following examples are presented to provide a more completeunderstanding of the invention. The specific techniques, conditions,materials, proportions and reported data set forth to illustrate theprinciples and practice of the invention are exemplary and should not beconstrued as limiting the scope of the invention.

Preparation and Testing of a Conventional Non-Woven Glass Fiber Mat

A non-woven glass fiber mat of types typically used as a facer forconventional gypsum board is prepared using a wet laid mat machine inthe manner disclosed in U.S. Pat. No. 4,129,674, which is hereinincorporated in the entirety by reference for all purposes. The mat,designated as comparative example 1, contains chopped glass fibers andis bonded together with a polymer binder. The specific materials usedare set forth in Table I. The M137 and K137 glass fibers arecommercially available from the Johns Manville Corporation of Denver,Colo. A conventional modified urea formaldehyde binder is applied with acurtain coating/saturation technique.

TABLE I Constituents of Conventional Non-Woven Glass Fiber MatsComparative Property Example 1 Fiber type K137 avg. length (mm) 19 avg.fiber diam. (μm) 13 amount (wt. %. of mat) 79 Binder type modified ureaformaldehyde amount (wt. %. of mat) 21

Standard tests for characterizing the physical and mechanical propertiesare carried out on the comparative example mat, including basis weightper unit area, loss of weight on ignition, and thickness. The testresults are summarized in Table II.

TABLE II Physical and Mechanical Properties of Conventional Non-WovenGlass Fiber Mats Comparative Example 1 Physical/Mechanical Property 1Basis weight (lbs./100 sq. ft.) 2.1 LOI (%) 21 Thickness (mils) 36.5Machine Direction (Tensile Strength lbs./3 in. width) 124 Cross Machine(Tensile Strength lbs./3 in. width) 84 Tabor Stiffness 45 FrazierPermeability (cfm/ft²) 625

Strengths are measured both along the web direction and across the web,using a conventional mechanical testing machine to determine the peaktensile strength of a sample about 7.5 cm wide. The stiffness isdetermined using the standard Taber stiffness test, wherein a 38 mm widestrip is deflected by applying force at a point 50 mm from a clampingpoint. The torque (in g-cm) required to achieve a 15° deflection isconventionally termed the Taber stiffness. Air permeability is measuredusing the Frazier test at a differential pressure of 0.5 inches of waterin accordance with ASTM Method D737.

Preparation and Testing of Exemplary Fiber-Reinforced Composite Mats

Fiber blends using fibers with a diameter of 8-14 μm are combined withmicrofibers to increase the smoothness and density of the fiberglassfacer mat produced in examples 2A-B. The present microfibers havediameters ranging from 0.5-6.50 μm, and are produced using a flameattenuated or rotary process. The microfibers may make up 5-30 wt. % ofthe total mat weight.

The fiber blends produce a dense, closed, uniform, and smooth facersheet which helps minimize gypsum bleed through, and provides protectionto the gypsum core. The fiberglass mats are produced with lower airpermeability and smaller pore size than the mats made in comparativeexample 1. Table III below shows the impact of different fibercombinations on the air permeability.

TABLE III Constituents of Exemplary Fiber-Reinforced Composite MatsProperty Example 2A Example 2B Larger avg. length (mm) 10 10 Fibers avg.fiber diam. (μm) 13 13 amount (wt. %. of mat) 80 80 Smaller avg. length(mm) 10 10 Fibers avg. fiber diam. (μm) 2.5 2.5 amount (wt. %. of mat)20 20 Binder Type Styrene Acrylic Styrene Acrylic Copolymer Copolymer +Water Repellant amount (wt. %. of mat) 21 21

The fiber-reinforced composite mats of examples 2A-B were tested for airpermeability using the Frazier test at a differential pressure of 0.5inches of water in accordance with ASTM Method D737. Table IV lists theair permeability measurement data and the rate of penetration for anaqueous gypsum slurry.

TABLE IV Physical Properties of Exemplary Fiber-Reinforced CompositeMats Avg. Slurry Basis Air Pore Penetration Weight Thickness Perm SizeTime Example (lbs/100 ft²) (mm) (cfm/ft²) (μm) (sec) 2A 1.7 20.3 23113.0 87 2B 1.7 19.9 233 12.9 485

The low air permeability of examples 2A&B correlate with longer slurrypenetration times. The addition of the a water repellant to the bindercomposition in example 2B was also helpful to increase the slurrypenetration time (i.e., lower the slurry penetration rate) by making themat more hydrophobic and hence more difficult for an aqueous slurry tomigrate through the mat.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Additionally, a number of well-known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent invention. Accordingly, the above description should not betaken as limiting the scope of the invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” includes aplurality of such processes and reference to “the facer” includesreference to one or more facers and equivalents thereof known to thoseskilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

What is claimed is:
 1. A fiber-reinforced composite mat comprising: a non-woven web of fibers, wherein the fibers comprise: a first group of fibers having an average fiber diameter from about 8 μm to about 25 μm; and a second group of fibers having an average fiber diameter from about 0.5 μm to about 6.5 μm; and a binder to bond together the non-woven web of fibers into the fiber reinforced composite, wherein the composite has an air permeability of 250 cfm/ft² or less.
 2. The fiber-reinforced composite of claim 1, wherein the air permeability of the composite is 250 cfm/ft² to about 150 cfm/ft².
 3. The fiber-reinforced composite of claim 1, wherein the air permeability of the composite is 250 cfm/ft² to about 200 cfm/ft².
 4. The fiber-reinforced composite of claim 1, wherein the air permeability of the composite is about 230 cfm/ft² to about 235 cfm/ft².
 5. The fiber-reinforced composite of claim 1, wherein the first group of fibers have an average fiber diameter of about 13 μm.
 6. The fiber-reinforced composite of claim 1, wherein the second group of fibers have an average fiber diameter of about 2.5 μm.
 7. The fiber-reinforced composite of claim 1 wherein: the first group of fibers comprise about 70 wt. % to about 90 wt. % of a total weight of fibers; and the second group of fibers comprise about 10 wt. % to about 30 wt. % of the total weight of fibers.
 8. The fiber-reinforced composite of claim 7, wherein the second group of fibers comprises about 20 wt. % of the total weight of the fibers.
 9. The fiber-reinforced composite of claim 1, wherein the thickness of the fiber-reinforced composite comprises about 10 mils to about 30 mils.
 10. The fiber-reinforced composite of claim 1, wherein the binder comprises a styrene-acrylic copolymer.
 11. The fiber-reinforced composite of claim 1, wherein the binder comprises a water repellant additive.
 12. The fiber-reinforced composite of claim 1, wherein the composite is a facer for a building material.
 13. The fiber-reinforced composite of claim 1, wherein the building material comprises gypsum board.
 14. The fiber reinforced composite of claim 1, wherein the fibers are selected from the group consisting of glass, mineral, wool, ceramic, carbon, metal, refractory materials, and mixtures thereof.
 15. The fiber reinforced composite of claim 1, wherein fibers are glass fibers selected from the group consisting of E glass, C glass, T glass, sodium borosilicate glass, and mixtures thereof.
 16. A gypsum board comprising: a fiber-reinforced composite facer affixed to at least one surface of the gypsum board, wherein the facer comprises: a non-woven web of fibers, wherein the fibers comprise: a first group of fibers having an average fiber diameter from about 8 μm to about 25 μm; and a second group of fibers having an average fiber diameter from about 0.5 μm to about 6.5 μm; and a binder to bond together the non-woven web of fibers into the fiber reinforced composite, wherein the fiber-reinforced composite facer has an air permeability of 250 cfm/ft² or less.
 17. The gypsum board of claim 16, wherein the gypsum board comprises two or more of the fiber-reinforced composite facers.
 18. A process for manufacturing a fiber-reinforced composite, the process comprising: blending a first group of fibers having an average fiber diameter from about 8 μm to about 25 μm with a second group of fibers having an average fiber diameter from about 0.5 μm to about 6.5 μm to form a non-woven web of fibers; contacting the non-woven web of fibers with a binder solution to form a wet mat; and curing the wet mat to form a fiber-reinforced composite mat, wherein the fiber-reinforced composite mat has an air permeability of 250 cfm/ft² or less.
 19. The process of claim 18, wherein the process further comprises applying an aqueous slurry to a surface of the fiber-reinforced composite mat, wherein the slurry comprises at least one material selected from the group consisting of calcium sulfate, calcium sulfate hemi-hydrate, and hydraulic setting cement.
 20. The process of claim 18, wherein the process further comprises: providing a first facer comprising the fiber-reinforced composite mat; distributing an aqueous slurry to form a layer on the first facer, wherein the aqueous slurry comprises at least one material selected from the group consisting of calcium sulfate, calcium sulfate hemi-hydrate, and hydraulic setting cement; applying a second facer onto the top of the layer formed from the aqueous slurry to form a laminate; separating the laminate into individual pieces; and drying the pieces, wherein the first facer provides a first face of the dried piece with a smoothness sufficient to permit the dried article to be directly painted.
 21. The method of claim 20, where the dried piece comprises a piece of gypsum board. 